The invention concerns a dialysis membrane of cellulose regenerated from a cuoxam solution, i.e., a cupric ammonium solution, in the form of a hollow fiber with a continuous hollow interior and a closed mantel line (i.e., periphery).
Hollow fibers exhibiting a continuous hollow interior and regenerated cellulose from cuoxam solutions are known, for example, from German Pat. No. DE-PS 736 321.
U.S. Pat. No. 3,228,877 discloses that fibers prepared according to DE-PS 736 321 are suitable as dialysis membranes and also for reverse osmosis.
Hollow fibers from cellulose regenerated from cuoxam solutions, exhibiting a defined membrane structure, a uniform wall thickness along the total fiber axis and a true circular cross-section are known from U.S. Pat. No. 3,888,771. In addition, these fibers are stretched and exhibit good tensile strength properties. Although an improved strength resulting from stretching is desirable, this deleteriously affects the swelling properties of the membrane, thereby reducing the effectiveness of the dialysis.
U.S. Pat. No. 3,700,545 describes multi-segment fibers, whereby in the reference FIGURES no hollow fibers are represented, but rather bi-component multi-segment fibers with "side-by-side", "eccentric core-mantel" and "centric core-mantel" arrangement.
U.S. Pat. No. 4,175,153 describes inorganic, monolithic hollow fibers. It is in connection with the extrusion of a polymer solution which contains inorganic material, indeed referring thereto, that also profiled spinning nozzles can be employed. However, circular-shaped spinning nozzles are expressly preferred.
During dialysis, for example, hemodialysis, it is necessary that the membrane wall can be contacted or surrounded completely and without hindrance by the dialysis fluid. When packed into bundles as dialysis membranes, the hollow fibers with true circular cross-sections, tend to associate closely together along their entire length, much the same as the so-called glass plate effect between two flat parallel plates. This phenomenon increase more seriously in bundles of such fibers which, for their intended use, may have fiber densities of between about 500 and 1000 per cm.sup.2.
Introduction of the dialysis fluid into the intermediate areas between the hollow fibers becomes more difficult on account of this fiber association, the surfaces at which the hollow fibers associate closely together remaining unused for the exchange process. As a result, the effectiveness of the hollow fiber module is reduced.
In hemodialysis, the effectiveness of a dialysis membrane depends on the ratio of the exchange surface to the volume and the concentration gradients at the sides of the membrane walls. Stream flow conditions in the membrane interior are also significant. During laminar stream flow, an outer layer forms along the membrane walls; this layer has a reduced concentration of metabolites. The resulting effect is a reduction in the exchange rate at a given concentration gradient. Until now, only hollow fibers with circular cross-section have been used. Those deviating from truly circular have been considered as deleterious.